Electrocatalytic sensing of NADH on a glassy carbon electrode modified with electrografted o-aminophenol film

A simple and sensitive method for the electrocatalytic detection of NADH on a glassy carbon electrode modified with electrografted o-aminophenol film (o-AP) is presented. The modification of a glassy carbon electrode surface with an o-AP film was achieved by electrochemical reduction of the corresponding, in situ generated nitrophenyl diazonium cation. The functionalized electrode shows an efficient electrocatalytic activity towards the oxidation of NADH with activation overpotential, which is ca. 350 mV lower than that at the bare electrode. The stability and the electrocatalytic activity of the modified electrode have been critically addressed. The formation of an intermediate charge transfer complex is proposed for the charge transfer reaction between NADH and adsorbed o-AP. The second-order rate constant for electrocatalytic oxidation of NADH, kobs, and the apparent Michaelis–Menten constant KM, at pH 7.0 were evaluated with rotating disk electrode (RDE) experiments, using the Koutecky–Levich approach. Using the o-AP-GC electrode, at an applied potential of +150 mV (vs. Ag–AgCl) with amperometric detection of NADH, a calibration range from 7.5 × 10−7 to 2.5 × 10−6 with a detection limit of 1.5 × 10−7 M was obtained, and excellent reproducibility was demonstrated with an RSD% = 2.1, n = 10 using a concentration of 1.0 × 10−6 M NADH.